Rotary fluid machines, such as turbines or pumps, have been developed to measure the quantity of fluid that flows past a point, or inject predetermined quantities of liquid additives into liquid flow streams. Such devices can be used, for example, to add materials such as iodine or io: chlorine to drinking water or liquid fertilizer concentrate to irrigation water. They frequently employ one or two rotors or vanes that rotate in a housing or flow conduit. Turbines frequently employ rotors having close tolerances between the ends of the blades and the stator, while pumps frequently employ rotors with ends that engage the housing.
Most rotary fluid machines experience a degree of leakage during ordinary operation. This leakage increases as the rotors began to wear. Leakage generally occurs in both the radial and axial directions with respect to the rotors. Seals have been provided to minimize leakage, but are not completely effective.
It is important that the leakage in a pump or turbine be minimized. The head pressure that a pump or turbine can deliver is largely determined by the efficiency with which the leakage around the seals can be controlled. In addition, in certain applications, contamination of fluids being pumped or metered must be avoided.
When the leakage around the seals becomes significant, the seals must be replaced. This is a difficult task, particularly because it is generally not clear which seals are leaking, thus requiring some seals to be replaced that were not leaking.